1. Field of the Invention
The present invention relates to a magnetic sensor, a production method thereof, a rotation detection device, and a position detection device, particularly to a magnetic sensor that detects a magnetic field while incorporated into a device for detecting rotation or position of an object.
2. Description of the Related Art
Conventionally, examples of a magnetic sensor used to detect rotation or position of an object include a Hall sensor in which the Hall effect is utilized, a GMR (Giant Magnetoresistance) sensor in which the giant magnetoresistance effect is utilized, and an AMR (Anisotropic Magnetoresistance) sensor in which the anisotropic magnetoresistance effect is utilized. The Hall effect is a phenomenon that when a magnetic field is vertically applied to a plate through which electric current is running, electromotive force is generated in a direction perpendicular to both the magnetic field and the current. Accordingly, in principle the Hall sensor cannot sense a magnetic field parallel to a substrate (thin film).
The GMR effect is a phenomenon that, when the current is running through a thin film having a three-layer structure (ferromagnetic material, non-magnetic material and again ferromagnetic material), a scattering probability of electrons flowing in the non-magnetic material layer is changed according to a relative angle of magnetization of the ferromagnetic material layers, and thereby electrical resistance changes. The AMR effect is a phenomenon that the resistance changes according to an angle formed between a magnetization direction of a magnetic film and a direction of the current running through the magnetic film. Examples of the magnetic film include Ni and Fe films. In the AMR film, a rate of resistance change to the external magnetic field is not too large when compared with the GMR film. However, unlike the GMR film, the AMR magnetic film has not the multi-layer structure but a monolayer structure.
GMR differs from AMR in the following points; (1) GMR has an incommensurably large magnetoresistance ratio, (2) GMR is independent of an angle formed between current flow and orientation of magnetic field during resistance measurement, (3) GMR has a complicated layer structure. Therefore, although a GMR sensor has the same purpose of the magnetic detection as an AMR sensor, the GMR sensor differs completely from the AMR sensor in the structure and action.
A magnetic sensor with a magnetoresistance element made of this kind of ferromagnetic metal uses the magnetoresistance effect possessed by ferromagnetic material. Namely, the magnetic sensor utilizes changes in electrical resistance when the distribution of electrons is distorted by a magnetic field, and electrons energetically stabilize and compensate the distortion. A magnetic sensor has magnetoresistance elements with a meandering structure where the angle formed between orientation of the applied magnetic field and the direction of the current running through the magnetoresistance element is 90°, and magnetoresistance elements with a meandering structure where the angle between orientation of the applied magnetic field and the direction of the current running through the magnetoresistance element is 0°. The magnetoresistance elements are connected serially, and the connection point of the magnetoresistance elements is connected to an input of a comparator circuit to recognize a difference voltage at a middle of the series-resistance structure and amplify it for magnetic detection.
The magnetic sensor receives a horizontal component of the applied magnetic field and detects the change in resistance of a thin-film magneto-resistor formed on an IC substrate. The magnetic sensor does not react to the external magnetic field applied from a direction (Z axis direction) perpendicular to the substrate. Four resistance elements arranged in different angles are formed in a bridge shape, the magnetic field is detected by a potential difference between the resistance elements, and a magnetic sensitive property depends on the direction (X-Y axes direction) of the applied magnetic field.
The magnetic field is referred to as operating magnetic field when the magnetic field is applied at an angle of 90° to the direction of the current running through the magnetoresistance element. On the other hand, the magnetic field is referred to as canceling magnetic field when the magnetic field is applied at an angle of 0° to the direction of the current running through the magnetoresistance element. The basic operation of the magnetic sensor will briefly be described with reference to FIGS. 5 and 6.
FIG. 5 shows a basic circuit configuration of a conventional magnetic sensor. Referring to FIG. 5, magnetoresistance elements 11 to 14 are formed in the bridge shape in a magnetoresistance element unit 10, and a comparator 21 and a feedback resistance 22 are arranged in an IC circuit waveform processing unit 20 so as to have comparison and amplification functions.
FIG. 6 shows the magnetoresistance element unit 10. The magnetoresistance elements 11 and 13 have continuous meandering structures that look like vertical strips, and are formed on the substrate. The magnetoresistance elements 12 and 14 have continuous meandering structures that look like horizontal strips, and are formed on the substrate. Among the four magnetoresistance elements 11 to 14, the magnetoresistance elements having the strips of the different directions are connected to each other to form a bridge.
In this case, the magnetoresistance elements 11 and 13 are resistors that respond to the operating magnetic field, and the magnetoresistance elements 12 and 14 are resistors that respond to the canceling magnetic field. When the magnetic field is applied from the left direction of FIG. 6, resistances of the magnetoresistance element 11 and 13 changes by the magnetoresistance effect, which results in a change in potential at a middle point 16 between the magnetoresistance element 11 and 14. Similarly the potential changes at a middle point 17 between the magnetoresistance element 12 and 13. Using a difference voltage between the middle points 16 and 17, the comparator 21 and the feedback resistance 22 in the IC circuit waveform processing unit 20 perform the comparison and amplification to detect the change in magnetic field.
The conventional package structure will be described with reference to FIG. 7. FIG. 7 shows a schematic configuration of the conventional magnetic sensor where FIG. 7A is a top view and FIG. 7B is a side view. The circuit shown in FIG. 5 is arranged on a semiconductor substrate 47, and the circuit has the magnetoresistance elements shown in FIG. 6. The semiconductor substrate 47 on which the thin-film magnetoresistance element is formed on the IC substrate is mounted on a lead frame 40, and the semiconductor substrate 47 is connected to lead frames 40 to 42 by wires 43 to 45 (wire bonding). The lead frames 40 to 42 act as a connection terminal to the outside of a mold-sealed package 46. The semiconductor substrate 47 is mounted in parallel with the surface of the package 46.
The thin-film magnetoresistance elements 11 and 13 respond to the magnetic field in the horizontal direction (X-Y axes direction) parallel to the package surface, i.e., the magnetic fields applied through package surfaces 46a and 46b, while the magnetoresistance elements 11 and 13 do not respond to the magnetic fields applied through package surfaces 46c and 46d. That is, the magnetoresistance elements 11 and 13 sense the magnetic field in the horizontal direction but cannot sense the magnetic field in the vertical direction.
In the conventional magnetic sensor, the magnetic fields applied through package surfaces 46e and 46f are recognized as the canceling magnetic field, and the resistance values of the magnetoresistance elements 12 and 14 are changed. Therefore, the magnetic sensor operates in a direction that the detection is cancelled. Detecting sensitivity of a magnetic sensor in the magnetic field varies depending on whether a magnetic field in the canceling direction exists or not. Therefore, in the conventional magnetic sensor, in the case of the presence of the canceling magnetic field, the influence of the canceling magnetic field cannot be compensated unless the magnetic field equal to or larger than the canceling magnetic field is applied in the magnetic-sensor operating direction.
A relationship between a resistance value of a magneto-resistor and an insertion angle of an applied magnetic field will be described with reference to FIGS. 8 and 9. FIG. 8 is a front view of the magneto-resistor when the magnetic field is applied in parallel (X-Y axes direction) with a surface of the magneto-resistor. FIG. 9 is a top view of the magneto-resistor when the magnetic field is applied while having an angle with respect to the surface of the magneto-resistor.
Conventionally, in a magneto-resistor 53 made of ferromagnetic material, a resistance change amount depends on an insertion angle 50 (θ in the following equation (1)) formed by the direction of the applied magnetic field 52 and current running through the magneto-resistor 53, as expressed by equation (1):ρ=ρ0−Δρ·sin 2θ,   (1)where ρ is a resistance value after the magneto-resistor 53 is changed, ρ0 is an initial value of the magneto-resistor 53, and Δρ is an amount of a resistance change of the magneto-resistor 53.
As shown in FIG. 8, the resistance change amount caused by the applied magnetic field appears directly as the change in resistance for the magnetic field when θ of the insertion angle 50 is set at 90°. On the other hand, Δρ becomes zero for the magnetic field that is applied where θ is 0°, and no change occurs. That is, the magnetic field applied at θ of 90° means that the magnetic field is applied in the operating direction, and the magnetic field applied at θ of 0° means that the magnetic field is applied in the canceling direction.
The case in which the direction of the applied magnetic field 52 has an angle (in the Z axis direction) relative to the surface of the magneto-resistor while θ of the insertion angle 50 is maintained at 90° in the X-Y axes plane will be described below. As shown in FIG. 9, when the magneto-resistor 53 is inclined by 45° toward the Z axis direction (inclinations 56 and 54 are set at 45° for example) while θ is maintained at 90° in the X-Y axes plane, a magnetic field component 55 in the X-Y axes direction, horizontal to the magneto-resistor 53, is 1/√2 times the value of the magnetic field 52. When a magnetic field 58 is applied from above the magneto-resistor 53, a magnetic field component 57 in the X-Y axes direction, horizontal to the magneto-resistor 53, is 1/√2 times the value the magnetic field 58. The magneto-resistor 53 detects the magnetic field 55 or 57 and operates based on the equation (1).
Japanese Utility Model Registration No. 2512435 (Document 1) discloses that a Hall element is mounted on a substrate of a peripherally opposing motor and is arranged while inclined relative to a magnet such that the surface of a magnetic sensitive unit of the Hall element intersects a main magnetic flux generated by the magnet. Therefore, the magnetic field is readily sensed to improve performance of the device. However, Document 1 does not disclose a resistance element made of ferromagnetic material, but only relates to a Hall element. Additionally, Document 1 does not aim to increase directions of magnetic field detection, but only tilts a Hall element so that a magnetic field is easily detected. Therefore, when the magnetic field is applied from another direction, there is no function of suppressing the influence of the magnetic field on the magnetic sensitive property.
Japanese Patent Application Laid-Open (JP-A) No. 8-338863 (Document 2) discloses that a recess is formed in an inner surface to locate the magnetoresistance element in the magnetic detection device arranged close to various motors to detect a rotational position or a revolving speed of a rotary body. Document 2 emphasizes accurate measurement where the resistance element is inclined to detect the clockwise or counterclockwise rotation of the rotary body including opposite permanent magnets. However, the purpose and the effect differ from the present invention.
JP-A No. 2004-128474 (Document 3) discloses a method of producing a two-chip-built-in magnetic sensor where two magnetic sensor chips are mounted on a stage of a particular lead frame to detect the magnetic field from three-dimensional directions. In the production method, the magnetic sensor is produced while the two magnetic sensor chips are inclined relative to the substrate. One of the magnetic sensor chips detects the magnetic field in the horizontal direction (X-Y axes direction), and the other magnetic sensor chip detects the magnetic field in the vertical direction (Z axis direction). Document 3 discloses the production method and differs from the present invention in that the magnetic sensor needs the magnetic sensor chips for the horizontal and vertical directions respectively. Additionally, because Document 3 seeks accurate measurement of the orientation and reduction of production cost, the objectives are different from the present application.
JP-A No. 2004-354182 (Document 4) discloses a thin-film magnetic sensor and a production method thereof. The thin-film magnetic sensor can detect the external magnetic field in the direction perpendicular to the surface of an insulating substrate. An irregular (bumpy) portion and a pair of thin-film yoke (collective name of iron and the like constituting the magnetic circuit) are formed on the insulating substrate, and the GMR film is formed in a gap between the thin-film yokes. Additionally, two sensor units are provided. That is, one of the sensor units detects the external magnetic field in the horizontal direction, and the irregular portion is formed on the substrate to incline the GMR film, which allows the other sensor unit to detect the external magnetic field in the vertical direction. Because the GMR effect is utilized in the technique, the technique differs from the present invention in the fundamental effect and the two-chip configuration.
A first problem with the conventional magnetic sensor is that the magnetic sensor responds to the horizontally applied magnetic field while not being able to respond to the vertically applied magnetic field. This is attributed to characteristics of the magnetoresistance element. Usually the thin-film magneto-resistor formed on the IC substrate responds to only the magnetic field that is horizontally applied through a package side face.
A second problem comes up from the design of a conventional magnetic sensor where the magneto-resistors each having the continuously folded structure are arranged so that vertical strip magneto-resistors and horizontal strip magneto-resistors are alternated. When the magnetic field is applied in the magnetic sensor's operating direction that forms an angle of 90° with the current running through the magnetoresistance element while the magnetic field of the canceling direction (an angle of 0°) is simultaneously applied, the influence on the canceling magnetic field cannot be compensated unless the magnetic field of the same intensity as the canceling magnetic field is applied in the magnetic-sensor operating direction.
The reason is that due to the orientation of the magneto-resistors having the continuously folded structures, even if the insertion angle of the applied magnetic field becomes 0° with respect to some of the magneto-resistors, the insertion angle to other magneto-resistors becomes 90° to respond to the magnetic field applied in the canceling direction. Therefore, the potential fluctuates at the connection point where the magneto-resistors are connected in series, and the input potential of the comparator circuit reversely changes. When a magnetic field is applied in the canceling direction while the operating magnetic field is applied, the sensitivity is changed and the original magnetic sensing characteristics of a magnetic sensor cannot be obtained. The problem cannot be avoided due to the structure of the sensor. Under the condition that the canceling magnetic field is applied, the magnetic field equal to or larger than the canceling magnetic field must be applied in the direction where the influence of the canceling magnetic field is compensated.